Honda F1 project leader Yusuke Hasegawa has outlined a number of reasons why Honda has been struggling so badly in the beginning of the 2017 Formula One season. He confirmed that lots of problems were not discovered while running on the dynamo meter.

Was this known prior to testing or was this boost noticed after anaylasing the testing data?

TR gave Honda extra space to redesign the exhaust manifold and as a result they gained 10Kw.

Source F1GP News(FujiTV)

Yes it was reported by Yoneya Mineoki-san that the extra space of the STR13 cowling and exhaust area intended for the Renault allowed Honda to revise their exhaust resulting in a 10Kw increase. He also mentioned some concern regarding race simulation pace -while on fresh tires their pace matches Renault but appear to be suffering more tire degradation possibly due to set up or driver skill. The early season strategy will be to let the front end of the midfield battle and suffer failures and stay close enough in the points paying positions to get bumped up after a few Renault DNFs.

The extra space did allow the exhaust to be revised but most of the gain was allowing the revising of the compressor to intake routing.

Wow. If 10kW is accurate, it's not insignificant, from a relatively minor (?) change. I mean, sure it's not massive, but it's not the single digit gains we sometimes hear about with various refinements. I wonder what the total bhp gain in Australia will be compared to the end of last year ?

Uhmm guys this is going way Off Topic again. This is a technical Topic about the PU itself. Not what Teams may or may not Run it in the Future. HPD's Post has been moved to the Team Thread, some OT Posts have been deleted.

It is indeed an EG civic! I linked it because of the trend with bonnet exit exhausts that was mentioned.

That particular example is from a company called JDMYard just down the road from me. That and their World Time Attack contender are all great pieces of engineering powered by K-Series engines. Porn for any Honda fan.